Rechargeable battery pack for a transport refrigeration unit

Abstract

Rechargeable battery pack A rechargeable battery pack (30), related methods and a transport refrigeration unit (10) in combination with a rechargeable battery pack. The rechargeable battery pack comprises a framework (20) by which the pack is mounted to the TRU in use and a battery compartment (40) for plural rechargeable battery cells (46). The framework includes at least one shelf (50) for supporting the plural battery cells in the compartment. The cells have a width, depth and height and the width is at least twice the depth. The cells are arranged on each shelf in plural groups of upright cells, each group arranged side by side on the shelf, and in each group the cells are arranged in a lateral orientation plural cells deep such that the overall number of cells form a cuboid volume on the shelf.

Description

[0001] RECHARGEABLE BATTERY PACK

[0002] The present invention relates to a rechargeable battery pack, related methods and to a transport refrigeration unit of a type configured to draw power from rechargeable batteries in cooling the interior of a mobile enclosure, such as in a trailer or lorry.

[0003] Rechargeable battery packs are known in many industries. Most of the development work to date has been in the field of Electric Vehicles. However, there are other applications where rechargeable batteries are to be used where approaches used in the EV field are not suitable or non-optimal.

[0004] To take one example, there have been recent attempts to provide transport refrigeration units that are powered by rechargeable batteries. Transport Refrigeration Units (TRUs) play an important role for the food distribution industry in delivering fresh, frozen, and other perishable food from field to market. These are used with small rigid vans / trucks right through to articulated trucks pulling a refrigerated container. Often, a TRU may be used with a tractor unit pulling a semi-trailer (known as a semi-trailer truck in the US, an articulated lorry in the UK and various other names in other countries), where the TRU is added to a specially designed and insulated trailer according to a particular customer's specifications. The TRU comprises a refrigeration system that, when driven, blows chill air into one or more compartments in the interior of the trailer to cool the contents.

[0005] Traditionally TRUs are diesel driven, particularly when used with trailers. Such units are well established in the industry, but have a number of drawbacks including noise and exhaust emissions. To address the inefficiencies associated with regular diesel-driven TRUs, some hybrid designs and eTRUs have been proposed using solar power and / or batteries to supplement and / or supplant other power sources in powering the refrigeration unit. More recently, the present applicants have proposed in PCT / EP2021 / 062825, filed 14 May 2021 , entitled "Electric Mobile Refrigeration Unit", the entire contents of which are hereby incorporated by reference in their entirety, a refrigeration unit powered by rechargeable batteries, optionally supplemented by solar, to minimise or eliminate the need for diesel power from the tractor unit or separate generator to power the refrigeration system. Despite the advent of battery powered TRUs, relatively little thought has hitherto gone into how to most effectively accommodate the batteries in such systems. Wherever they are positioned, batteries must be secure and protected from the elements. Typically batteries are heavy and require a strong support framework. Accessibility is an important concept in battery placement, e.g. for serviceability. Also efficiently packing batteries is important, to avoid taking up space that could otherwise be used for other purposes. The envelope available to a TRU is tightly constrained by its positioning and attachment to the container to be cooled. Accordingly, it has been proposed to place batteries in racks under the trailer. However, such arrangements have the disadvantages that the space under the trailer is often already used for other purposes and that provisioning and fitting the system to a trailer becomes more difficult, as separate units are required for the TRU containing the refrigeration system which sits at the front of the trailer, and the battery rack under the trailer, with connections between them then needing to be made. Furthermore no standards currently exist for battery racking systems underneath the trailer or indeed anywhere else, meaning a TRU manufacturer must collaborate with trailer manufacturers in provisioning a suitable racking system for each specific trailer, rather than being able to ship a unit that complies with the relevant standards which can be relied on to integrate with any compliant trailer and so can be shipped and fitted by the end user of the trailer.

[0006] Other considerations are the need to thermally manage the batteries, keep them free of moisture and dirt, protect them from damage through collision, vibration or shocks, manage the interconnects and battery management functions and maintain the proper orientation for optimum performance as dictated by the battery cells being used. The weight of the batteries must also be properly supported and transferred to the trailer. Consideration should also be given to ease and cost of manufacturing the unit, reliability, as well as maintenance and servicing the units in the field.

[0007] It should be noted that it is known in the prior art for diesel driven TRUs to include small batteries to power the electronics and start-up of the refrigeration system. However, these batteries are small and not intended or capable of providing the main source of power to the refrigeration system, and so the fitting such a small battery into the confines of the TRU or achieving high battery densities becomes less of a concern. The present disclosure is concerned with battery packs suitable for providing the TRU's primary source of power, possibly supplemented by solar or other sources, and it is desired to incorporate a large volume of battery power capable of driving the refrigeration system, i.e. as sometimes called "traction batteries", into the TRU itself in an optimum way.

[0008] The present invention aims to address these and other problems in the prior art both in the field of transport refrigeration units and in other applications where rechargeable batteries are used to power a mobile device.

[0009] According to a first aspect of the present invention, there is provided a rechargeable battery pack for a transport refrigeration unit (TRU) , the pack comprising: a framework by which the pack is mounted to the TRU in use; a battery compartment for plural rechargeable battery cells, the framework including at least one shelf for supporting the plural battery cells in the compartment; wherein the cells have a width, depth and height and the width is at least twice the depth, wherein the cells are arranged on each shelf in plural groups of upright cells, each group arranged side by side on the shelf, and in each group the cells are arranged in a lateral orientation plural cells deep such that the overall number of cells form a cuboid volume on the shelf.

[0010] As discussed, the space within the TRU and hence battery pack is typically shallow, such that a dedicated volume for the batteries will also be relatively shallow, i.e. having a smaller depth than its width or height dimensions. Typically the battery modules are prismatic, i.e. cuboid in shape, such that multiple modules of the same dimensions can efficiently be packed in an array, i.e. one or more row and one or more columns of batteries in a cuboid overall battery volume.

[0011] By orientating the battery cells laterally, this allows multiple battery cells to be stacked in a group of cells front to back. As the battery depth is the smaller dimension of the cell, stacking the cells in this way allows the overall depth of the group of cells to be more closely tailored to the optimum depth as per the constraints of the TRU. For comparison, if the cells were positioned "end on" on the shelves (e.g. like books on a book case), then the overall depth would be highly dependent on the width of the battery cell (as it would typically be difficult to fit more than one cell deep on the shelf) which might lead to wasted space. Thus, it is preferred to orientate the battery cells so their shorter dimension aligns with the smaller depth dimension of the TRU.

[0012] In an embodiment, the cells are 4 deep in a group and there are up to 8 groups per shelf.

[0013] In an embodiment, the cells have dimensions of approx, (within 2%) 174mm width, 204mm height and 54mm depth.

[0014] The above arrangement can give rise to highly efficient packing arrangements in which efficiencies of >95% can be achieved.

[0015] In an embodiment, the cells within a group are arranged in a housing, having flanges extending at the front and rear faces of the housing by which the group of cells is mounted to the shelf.

[0016] In an embodiment, at least one shelf comprises plural, vertically spaced shelves on each of which the battery cells are so arranged.

[0017] In an embodiment, the battery pack has vertical structural side members between the shelf or shelves extend.

[0018] In an embodiment, the pack has a front and rear cover to seal the battery compartment.

[0019] In an embodiment, the shelves have a fluid flow channel running through them by which the battery cells are cooled in use.

[0020] In an embodiment, fluid movement devices are mounted to the side of the battery pack to provide fluid flow for cooling the battery cells.

[0021] In an embodiment, there are mounting points at both sides of the structural framework for mounting the battery pack to a TRLI or trailer, wherein the mounting points are between 1 ,7m and 1 .85m apart and the battery cells do not extend laterally as far as the mounting points.

[0022] In an embodiment, each shelf has a capacity of at least approx. 23.5kWh. In an embodiment, the overall battery pack has a capacity of at least approx. 71 kWh. These values assume using 736Wh cells. In the future cells of similar dimensions may increase their capacity by 10 to 20 % such that these values will likewise increase. In an embodiment, 8 groups of cells on each shelf are arranged as 2 subgroups of 4 groups of cells, wherein the groups of cells in each subgroup are electrically connected in series.

[0023] The shelves may have a joint function of supporting the weight of the battery cells mounted thereto, allowing rows of battery cells to be stacked vertically on plural shelves of the framework, and providing thermal management to the battery cells by moving cooling fluid through the channels in the shelves such that heat from the batteries is drawn into the channels from the top face of the shelves in contact with the battery cells and dissipated. This allows high density of battery cells in the battery pack.

[0024] The cells may be stacked according to the needs of the application, i.e. to meet the requirements of voltage / capacity of the device being powered. The cells may be stacked into modules, i.e. cell stacks arranged in series and / or parallel in a housing to protect the cells, and the modules may be stacked into module stacks, e.g. connected in series and / or parallel with BMUs or other services supplied per battery module stack. Modules / cells preferably the same size and / or orientation. The cells are preferably vertically mounted in use such that the cells each have a face in contact with the bottom of the casing / heat plate, which is in turn in contact with the shelves allowing the shelves to thermally manage the cells. Also, some battery cell designs require vertical orientation for their performance. Preferably the terminals of the battery cells or battery modules (where organised in modules) are at the top. NB orientation is given by the shelves supporting the weight of the battery modules, i.e. the battery modules are on top of the shelves in use defining the vertical direction. In most applications, the battery cells will be disposed laterally across the shelves, and the fluid channels will also be aligned with this lateral direction, which will in most cases coincide with the larger dimension of the pack, i.e. the pack is elongate laterally, i.e. in its width, compared with its depth. The battery packs will generally be vertically mounted in use, e.g. to a vertical wall or framework of the device that is to be powered by the battery pack.

[0025] This is particularly useful where the pack is for powering and being accommodated in a TRU or similar technology. The design of trailers, their attachment to tractor units and various standards applicable to trailers place various constraints on the dimensions and layout of a TRU, i.e. it has typically a shallow box shape, i.e. depth dimension smaller than other dimensions, with a flat, generally rectangular back face for placing up against the wall of the enclosure and a flat, generally rectangular, but possibly curved (due to the enclosure pivoting), front face, which in use is fixed in the vertical plane when attached to a side wall of the enclosure, e.g. trailer or lorry. The TRLI framework may define a first volume in which the refrigeration system is located and a second volume below in which the battery pack is mounted are located, typically below. This provision of a dedicated volume in the TRU for batteries is preferable to optimise the packing of batteries and make maximum use of the limited space available in the TRU that is not needed for other components, e.g. the refrigeration system. The battery pack may be adapted to fit in the available volume, maximising use of space whilst still allowing access to the necessary components such as fans, contactors, chargers, for use and servicing.

[0026] The battery framework comprises structural members that are generally permanently fixed together, e.g. welded metal members, to increase the structural integrity. Preferably, the area through which batteries are accessed is unobstructed by members of the framework, i.e. when constructing or maintaining the unit, the battery can be offered up to the position in which it is ultimately fixed to the shelf unobstructed by members or neighbouring batteries in that layer of batteries. This may for instance comprise of advancing the battery modules into the space allocated for the battery on the shelf from the rear of the battery framework (or possibly the front) before fixing it in position. The framework may have fixing means by which it is fixed to the device it is intended to power in use. These fixing means, which may be for example holes in the framework by which bolts or other fixings can be used to attach the framework to the device, are outside the battery compartment, e.g. at the sides and or top and bottom of the framework. When used in a TRU system, the battery pack may include structural framework members for directly mounting to a truck or trailer, as well as to the refrigeration system pack, i.e. the part of the overall TRU containing the refrigeration system. Alternatively, the battery pack may mount to a unitary structural framework o the TRU, which also supports the refrigeration system, and this framework mounts to the truck or trailer.

[0027] In embodiments the TRU refrigeration system is capable of running solely on battery power from the batteries in the TRU (optionally supplemented by solar) to cool the enclosure for a journey, without any power input from an ICE, axle re-gen systems, or batteries mounted external to the TRU), although in other embodiments, other power sources may be used to supplement the batteries in the TRU. Thus the invention is advantageous in making efficient use of available space in a TRU, particularly where the battery capacity is large, e.g. preferably the battery capacity of the TRU for powering the refrigeration system may greater than 20kWh, or in some examples greater than 60kWh, or in some further examples, greater than 120kWh.

[0028] The battery pack is arranged to be sealed and dry, i.e. to protect and / or seal it from the wider environment, to prevent water, dirt or other liquids entering the compartment that may be encountered during use so that water / liquids cannot penetrate. The battery pack may have one or more covers (e.g. front and / or rear) that cooperate with the framework to completely enclose the battery compartment and that are removable to allow access to the battery cells, e.g. during manufacture or maintenance. The first and second compartments in the TRU may therefore be made open the environment to some degree, which is typically needed so that external airflow can reach components of the refrigeration system and or battery thermal management system. This also simplifies the manufacture of the TRU as no special measures are needed to separate the first and second compartments and keep the second compartment isolated.

[0029] In an embodiment, the battery modules are arranged in an array of plural rows and columns.

[0030] In an embodiment, the rechargeable battery pack is arranged to power a transport refrigeration unit for a truck or trailer, wherein either i) the battery pack framework is arranged to attach to a refrigeration system pack forming a transport refrigeration unit, wherein at least the battery pack framework mounts to the truck or trailer, or ii) the battery pack is arranged to attach to a TRU framework that also supports a refrigeration system, and the TRU framework attaches to the truck or trailer.. Thus, the TRU can be split into two separate packs, a refrigeration system pack and a battery pack, which can be attached together, and which both include structural framework elements for fixing to the truck / trailer. Alternatively, the TRU can have a unitary framework to which the refrigeration system and the battery pack are mounted, and this unitary framework is then attached to the trailer or truck.

[0031] In a further aspect, the invention extends to a method of providing a temperature controlled payload at a destination using the unit of described above, comprising powering the refrigeration system with the battery pack to control the temperature of the payload in the mobile enclosure whilst transporting it to the destination.

[0032] It will be appreciated that any features expressed herein as being provided “in one example” or “in an embodiment” or as being “preferable” may be provided in combination with any one or more other such features together with any one or more of the aspects of the present invention.

[0033] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 shows a perspective view of an example from the front of an example of a TRLI according to an embodiment of the invention;

[0035] Figure 2 shows a front view of the TRLI of Figure 1 with the TRLI outer covers removed and Figure 2b shows the TRLI with the battery pack removed;

[0036] Figure 3 shows a perspective view of an example of a battery pack according to an embodiment of the invention for use with the TRLI of Figure 1 ;

[0037] Figure 4 shows a front view of the battery pack of Figure 3 with the front cover removed;

[0038] Figure 5 shows a perspective view of a framework for the battery pack of Figure 3;

[0039] Figure 6 shows a perspective view of a shelf from the framework of Figure 5;

[0040] Figures 7a and 7b show another example of a refrigeration system pack and battery pack for a TRU according to an embodiment of the invention;

[0041] Figure 8 shows a stack of cells incorporated into a module;

[0042] Figures 9 to 1 1 illustrates the constrains imposed on the volume available to accommodate the TRU and battery cells and the relationship between width and depth of the maximum volume available;

[0043] Figures 12 to 14 show the preferred layout of battery cells in the battery pack according to an embodiment of the invention, with Figure 12 showing a lateral cross sectional view through shelf of battery modules, Figure 13 showing a perspective view of the battery pack with a battery module highlighted and Figure 14 showing a side view of the battery pack with a battery module highlighted; and

[0044] Figure 15 shows possible values for the Area A to be used by the battery cells. Figure 1 shows a perspective view of an example of a transport refrigeration unit 10, attached to the front of a semi-trailer 12 of the sort that can be attached to and pulled by a tractor unit (not shown) to transport goods loaded to the interior of the trailer via doors at the rear of the trailer, where the TRL1 10 implements a system for refrigerating the interior of the trailer. (Generally in the following description references to the “front” are in the direction of arrow 16, i.e. the forwards direction of the trailer; the “rear”, arrow 17; the “top”, arrow 18; the “bottom”, arrow 19 and the “sides”, numerals 15.) It will be appreciated that the TRU may equally be attached to other vehicles types, such as rigid body trucks, vans and lorries, or containers such as shipping containers that can be lifted onto a trailer for transportation and may be generally applicable to cooling the interior of any enclosure. Although the unit has been described as cooling the interior of the trailer, it may also be arranged to heat the interior of the trailer.

[0045] The TRU 10 comprises a structural framework 20 (shown separately in Figure 2B) which supports the various elements of the unit and which provides attachment points 20c for fixing it to the trailer, which are generally provided at the sides, e.g. in vertical side members 20a. The framework 20 generally defines an upper volume 22 and a lower volume 24. The upper volume 22 has an external cover (not shown for clarity) and houses a vapour compression refrigeration system 28 (shown in Figure 2B but omitted in Figure 1 for clarity) comprising primarily the evaporator 28a, compressor 28b, condenser 28c, and expansion valve 28d, together with fans 28e for moving air over the evaporator and condenser. When the compressor and fans are driven, these combine to blow chilled (or heated) air into the interior of the trailer 12 through an aperture 26 in the end wall of the trailer 25 to cool (or heat) the content, as is generally well known in the art.

[0046] The lower volume 24 houses a rechargeable battery pack 30 for powering the refrigeration system. An external cover of the TRU, here in 3 sections 32a, b,c, covers the battery pack. TRU cover is for instance plastic, with separate portions covering the battery compartment area, and the two side areas to allow access to components in the side areas without removing the entire cover. These covers are largely aesthetic and preferably unnecessary to keep the battery modules free from moisture.

[0047] Figure 2 illustrates the TRU without the external cover showing the battery pack 30 fixed, preferably removably, to the framework 20 by fixtures 34 connecting flanges at the sides of the battery pack with lower vertical side members 20b sections of the framework. Crash barriers 37 may be installed above and / or below the battery pack mounted to the TRU 20 framework to protect against impacts to the exposed face of the battery pack. Figure 3 shows the battery pack dismounted from the TRU framework 20.

[0048] In the example of Figures 1 and 2, a unitary structural framework 20 is used for the TRU to which the battery pack mounts. Alternatively, as shown in Figures 7a and 7b, the framework 20 may be provided in separable parts 20a, 20b, split between the upper volume and lower volume. For instance, the lower part of the framework, e.g. vertical side members 20b, which support the battery pack may be separate from the upper part of the framework 20a which supports the refrigeration system. The lower part of the framework may now be incorporated into the battery pack 30 itself. For instance, in the present example, the flanges at the sides of the battery pack are permanently fixed (e.g. welded) to the lower vertical side members 20b. Joining flanges 20e are provided by the battery pack for fixing to the upper part of the framework 20a at points 20f (or the upper framework for fixing to the lower framework, or both) to structurally connect the two parts. Thus, in effect, a refrigeration system pack and a battery pack are provided which may be connected together to form the TRU, both of which incorporate structural elements with attachment points 20c for mounting to the truck or trailer via fixtures. This arrangement of incorporating structural members into the battery pack 30 by which it is directly attached to the trailer may increase the structural integrity of the battery pack so the battery pack is better able to remain fixed to the trailer face in the event of a crash. In other respects, the example of Figures 1 and 2 and the example of Figures 7a and 7b may be the same.

[0049] As described more fully below, the battery pack 30 comprises a structural framework 33 defining within a battery compartment 40 including plural battery modules 41 . Front and rear covers 35,36 cooperate with the framework to seal the battery compartment such that moisture cannot penetrate to the battery modules. The framework provides structural support to the battery pack including i) mounting the battery modules inside and other components, and ii) allows it to be attached to the TRU framework 20 via the fixtures 34 in the example of Figures 1 and 2 or to be attached to the upper framework 20a and to the trailer in the example of Figures 7a, 7b., and iii) to be lifted into position for mounting / dismounting via lifting features 38. Fan units 62 forming part of the thermal management system 60 of the battery pack are positioned at one side of the battery pack, connectors 70 for making contact with the battery pack are positioned at the opposite side. Chargers may be conveniently mounted to underneath the battery pack for charging the batteries (e.g. from AC grid when at the depot and / or from solar power attached to the trailer in transit or at the depot), providing power to the refrigeration system 30 (i.e. to drive the compressor and fans) and / or exporting power from the batteries to the grid at the depot.

[0050] The TRL1 10 also comprises control electronics, communication means 29 for transferring data with a remote service that can manage or monitor the TRU, a III by which an operator can control the TRU, connectors for connecting to solar panels on the roof of the trailer or shore power when the trailer stationary. These may be mounted to any suitable point in the framework and communicate with the battery pack via connectors 70 and the refrigeration system.

[0051] Figure 4 shows the battery pack 30 with the front cover 35 removed. In this example, there are 3 rows 44a, b,c of 8 battery modules 41 in the battery pack. A battery module / stack of cells is shown individually by Figure 8, and comprises a stack of plural battery cells in a housing 48 strong enough to be handled / mounted. The housing may have flanges 49, e.g. extending from the front and rear faces of the module, by which the module can be fixed to the shelf. The battery module has positive and negative terminals 43a, 43b at the top by which connection 42a, 42b can be made to the module.

[0052] Each row 44 of battery modules 41 is supported by a shelf 50a, b,c running laterally across the battery pack, i.e. in a left right direction. The shelves are connected at the sides to vertical left and right side members 52a, b. The side members are generally L-shape in cross section, one leg attaching to the shelves and one leg extending laterally away from of the battery compartment providing a flange for attaching to the main body of the TRU via fixtures in the example of Figures 1 and 2, or being attached to the vertical side members 20b in the example of Figures 7a, 7b. Optionally, cross plates 51b may be included to brace the two legs, whilst generally keeping the space open for access to components mounted here (as described below). Alternatively or additionally the shelves themselves may have an extending portion 51 a at their ends that is welded to the lateral leg to help brace the side members. A top member 54 runs across the top of the battery pack also connected at the sides to the left and right side members. The shelves, top member and top member form a structurally rigid battery support framework 20. Further members 53 may be provided between the shelves to brace the framework. The framework also has lifting features 38, for instance towards the top of the framework at the sides, arranged for, say, a forklift to lift the battery pack and manoeuvre it, i.e. offer it up to the TRU framework for attachment and removal. The elements of the framework may be welded together, or using other structurally strong attachment method, to create a waterproof connection. Figure 5 shows the framework in isolation.

[0053] The front and rear covers 35,36 are attached, preferably removably by fixings, to the side members, shelves and top members at least around the periphery 56a,b,c,d of the open front face 56 and the periphery 57a,b,c,d of rear face 57 to help brace and structurally strengthen the assembly and also create a seal such that the battery compartment within is kept dry in use, i.e. sealed from ingress of rain, spray and dirt from the road, condensation in the refrigeration compartment, e.g. to within IP67 standard, or any appropriate standard. The covers may also be fixed to sealing faces at the front and / or rear of any intermediary shelves, which may help to further brace and structurally strengthen the assembly and / or such that each row of battery cells on a shelf is isolated from each other row. The rear cover 36 may be thin aluminium sheet. The front cover 35 may be aluminium or plastic and may be bowed outwards to make use of the additional space in the centre of the TRU envelope (see Figure 15) in order to accommodate additional components at the front of the battery pack in front of the battery modules.

[0054] A two stage venting system may be provided in the battery compartment 40. In stage 1 , a flex vent regulates pressure changes due to fluctuating temperature / altitude change. In stage 2, a burst vent regulates in case of battery venting. These may be provided on the front cover 35 of the battery pack (not specifically shown).

[0055] Battery chargers 80 are mounted to the underside the bottom shelf, with their connectors being accessible when the battery pack is mounted to the TRU framework. The framework may have additional structure 59 extending downward below the bottom shelf surrounding the volume occupied by the chargers at the sides and rear to protect the chargers and or provide a structure to allow the battery pack to be positioned on the ground.

[0056] Subgroups of battery modules 41a-d may be electrically connected together via interconnects 42, i.e. in series, positive terminal 43b to negative terminal 43a in a battery module stack. The positive and negative terminals of each battery module stack 41 , i.e. the end terminals in the series connected battery modules, are then connected in parallel via interconnects (shown in Figure 4) to respective positive and negative busbars which are mounted to the front of the shelves. The modules may for instance provide 12V and each module stack and thus the overall pack may provide 48V. It will be appreciated that the battery cells may be stacked in many different ways. Fuses may be provided within the series of interconnects / busbars to protect the circuit. Each module busbar is connected to a respective high voltage / current connector that passes through a side member 52 of the battery framework 33 through a sealed grommet / gland to maintain the waterproofing of the battery compartment and may connect to contactors allowing current to / from the battery pack to be switched by the control system of the TRU to isolate the battery pack. Thus, external high current connection can be made to the battery pack via the contactors for charging and for powering the refrigeration system / exporting power via suitable cabling.

[0057] A battery management unit (BMU) 75 is provided for each battery module stack 41 fixed to the front of the shelves 50. As is generally known, a function of a BMU is in balancing the battery cells when charging by bleeding off current from high-voltage / SoC cells (i.e. weaker cells having a smaller capacity that are charged faster) through a resistor so the cells in the module look like they have the same capacity. The BMUs connect to the battery cells via connectors 43c (shown in Figure 8) at the front of the battery modules and are connected by a harness to a low voltage / current connector at the side of the battery pack through which external connection can be made for controlling and powering the BMUs.

[0058] It is generally preferred to mount the busbars 45 and BMUs 75 at the front of the pack to the shelves, as the volume occupied by the battery modules will generally be a regular flat cuboid, i.e. constant depth, whereas the envelope available for the TRU will have a curved front surface due to the fixed distance (R) from the king pin of the trailer (see Figure 15) leaving usable space at the front between the battery modules and the front of the TRU at least in the central region.

[0059] Figure 6 shows a shelf 50 in isolation. The shelves are responsible for removing heat from the battery modules as well as from the battery management units and thus form part of the thermal management system 60. The shelves include channels 67 running laterally through them, i.e. in a left / right direction. The side members have apertures 68 (shown in Figure 5) communicating with the channels 67. Fan units 62 are positioned at outboard of the left hand side members 52a (equally the positioned could be reversed to be at the right hand side of the unit, but generally they are at the opposite side to the connectors so the connectors are not obscured, whilst both connectors and fans are conveniently situated and accessible) to draw air 66 through these channels to provide a cooling airflow. A plenum 69 is formed between the fan units 62 and the apertures 68 in the side members 52. At the opposite side, air is drawn into the channels through the apertures 68 in the side member. As the shelves 50 are welded to the side members (or otherwise fixed in a sealed fashion) around their periphery, these apertures only allow air into the channels 67 in the shelves and do not allow a path into the battery compartment, i.e. the waterproofing of the battery compartment is not compromised.

[0060] The battery heat load 64 is absorbed from the top face of the shelf 50, which is in close thermal contact with the bottom surface of battery stacks, and the BMU heat load 65 is absorbed by a BMU heat dissipation face at the front of the shelf where the BMU is fixed, e.g. with a BMU resistor in thermal contact with the shelf. The heat is transferred to the airflow and dissipated outside the battery pack. The shelf may also house heaters, which when supplied with current may be used to heat the batteries when operating in low ambient temperature conditions to a preferred operating point. There is preferably between 1 and 5 mm clearance between battery modules on a shelf when mounted.

[0061] It will be appreciated that it is generally desirable to maximise the battery capacity of the TRU but the space available for battery cells in the TRU is limited and subject to various constraints. Thus, efficient packing of battery cells in the battery pack is a key consideration. It will be appreciated in principle the battery cells may be stacked in many different ways. For instance, different arrangements and numbers of battery cells, modules may be provided to provide the necessary voltage and capacity. The number of cells in a module may be varied. So-called “Cell to Pack” technology could be used to mount cells individually to the shelves without housing them in a battery module. Different numbers of shelves of modules can be used depending on the desired battery capacity, and so on. Thus, there are many design options. Figures 9 to 13 illustrate a preferred packing arrangement.

[0062] Figure 9 shows from above the TRU 10 installed on a trailer 12, where the radius from the kingpin R sweeps out a volume on the face of the trailer which constrains the volume of the TRU. As discussed above, the volume occupied by the battery cells / modules will generally be a regular flat cuboid to best fit within this space. In addition, space must be left for the other components of the battery pack such as the structural elements, electronics, fans, chargers, etc. The battery cells are preferably in an upright orientation when the stacks are fixed in the pack. This is because, for at least some battery cell arrangements, it is important for battery performance to have an upright orientation to avoid some of the battery plates potentially being starved of electrolyte. Also, for thermal management, it is advantageous to have each battery cell in contact with the lower face of the battery module, which may be a thermal plate, to manage heat load dissipation from the battery cells. It is generally also convenient to use cells of the same type, e.g. size / voltage / capacity and battery modules that are the same in size, voltag e / capacity, and arrangement of cells within.

[0063] Figure 10 shows the dimensions of a cuboid volume to fit within the constraints of the TRU as mentioned above and Figure 11 shows the relationship between volume V and the width W using typical dimensions for a TRU. The depth D of the battery module can be established as a function of the width W by the following equation (based on Pythagoras' theorem), i.e.:

[0064] 1 ) D = SQRT ( R2 - (W / 2)2 ) - L

[0065] Thus, the Area A is given by W . D, i.e.

[0066] 2) A = W . (SQRT ( R2 - (W / 2)2 ) - L) and the Volume V is given by H . A, i.e.

[0067] 3) V = H . W . (SQRT ( R2 - (W / 2)2 ) - L)

[0068] Figure 11 plots this relationship with the maximum allowable radius from the kingpin R = 2.04m, the distance from the kingpin to the front of the trailer L = 1 ,6m and the height of the battery module H is 0.9m.

[0069] It can be seen from Figure 9 that the depth D of the battery modules is important in maximising the available volume V given the curved front surface of the available volume dictated by the maximum radius R from the kingpin 200. In particular, the depth of the battery modules determine the point 201 where the edges of the battery pack volume meet the curved surface of the TRU volume. If they are too deep, then battery modules cannot extend very far towards the sides and can only be positioned centrally where the volume has maximum depth, and so the overall battery volume is curtailed by the lack of width (W). Conversely, if the battery modules are thin, they can extend further towards the sides whilst staying in the available volume, but the overall battery volume is now curtailed by the lack of depth (D). It can be seen from Figure 11 that for a cuboid volume, an optimum depth can be found between these extremes that maximises the battery volume in the available space.

[0070] Similarly, it can be seen that, where the choice of battery depth D is limited, equation 1 can be rewritten so the width W is in terms of the depth D, and hence similarly equations 2 and 3 can be rewritten to give the Area A and Volume V in terms of the depth D. Accordingly, the Volume can be plotted as a function of depth D, and the optimum Volume obtained for the battery depth D or depths that are available, from which the width W is then obtained via equation 1 .

[0071] Figure 15 shows the optimum value of W and hence A for various values of D. It can be seen that to achieve the maximum Area (row 300), the optimum width of the battery volume is approx. 1511 mm and the optimum depth is approx. ,295mm. In most cases, good results may generally be obtained by using a width W that is within 10% greater or lesser of the optimum value obtained in this way, i.e. the Area will still be within approx. 2% of the maximum Area.

[0072] However, this maximum is not always achievable in practice because the depth D and width W parameters are fundamentally a function of the dimensions of the cells, i.e. an integer multiple of the width, height or depth of the individual cells chosen. It may be desired to use off the shelf cells with standard sizes making it difficult or impossible to achieve or come close to the maximum. Furthermore, various structures must in practice be provided to protect and support the cells which must also be accommodated within the overall Volume V. The present example seeks to achieve battery capacity close to the maximum whilst using standard cells.

[0073] In the present example, prismatic LFP cells are used, which have very standardised sizes. Typical 3.2V cells commonly come in sizes (allowing for 1 mm tolerance in width height and 3mm on height) shown in this table: Nominal Typical

[0074] Capacity Application Width Height Thickness

[0075] 100 / 125Ah Light commercial vehicle 200mm 172mm 33mm

[0076] 202 / 228 / 230Ah Heavy commercial vehicle & bus 174mm 204mm 54mm

[0077] 280 / 314Ah Stationary Energy Storage (ESS) 174mm 204mm 72mm

[0078] * It will be appreciated that capacities tend to increase over time as battery cell technology improves such that it might be expected that battery cells of similar dimensions could increase their capacity by 10% or 20% in the future.

[0079] Figure 14 shows a lateral cross section through a group of cells on a shelf in the battery pack within the Volume V. The cells 46 in the battery pack are organised as up to 8 stacks of cells (modules 41 ) side by side on each shelf, with the cells 46 in each stack arranged laterally 4 deep back to front. The cells are selected from the second row of the table above and have a width of 174mm x height of 204mm x depth of 54mm. As shown by Figures 12 and 13, there are 3 shelves in the battery pack in this example.

[0080] With the cell orientated laterally, 4 cells front to back gives a depth of 4 x the cell thickness (4 x 54mm = 216mm) plus tolerances and clearances of e.g. 9 mm cumulative between the cells, 50mm for the housing / flanges (48,49) at each end of the module and 10 mm for the covers 35,36 at the front and back of the pack which gives 285mm thickness. Figure 15 shows that this depth 302 gives a maximum width W of approx. 1560mm.

[0081] The width of the cell is 174mm and allowing for 2mm for the module housing 48 and 2mm clearance and tolerance per cell, allows 8 cells at 1424mm. As discussed above, the battery pack will have structural side members 52a, 52b outboard the outermost modules to which the front and rear covers 35,36 attach and seal along faces 56b,57b / 57,57d which must be accommodated within the Area A. (NB the front face may bow 250 outwards in the centre to help accommodate electronics and other items within the battery pack.) Allowing 50mm for these side structures, this gives a width of 1474mm. Figure 15 shows that this approx, width 304 gives a maximum depth D of 300 mm.

[0082] Thus, the width and depth are both very close to the optimum values, giving an achieved useful area of approx. 95%. Where 230Ah cells are used, which at a nominal voltage of 3.2V equals 736Wh per cell, the 32 cells for each shelf provides a total of 23.5kWh (7.36kAh).

[0083] Another advantage is that space is left at the sides of the battery pack for other structural elements and mounting fans, etc. For instance, a typical TRU mounts to the trailer at mounting points that are approx. 1 ,78m apart. This presents a possible upper limit on the width W (308) of the Area usable by the battery cells, as in general it will be desirable to have unobstructed access to the fixing points on the battery pack such that the battery cells should not extend this far to the sides. In the present example, it can be seen that there is approx. 30 cm space between the sides of the battery cells and the fixing points to accommodate fans and additional elements (it being appreciated that these will have to be less deep than the battery area A due to the tapering space at the sides of the battery pack.

[0084] Thus, the preferred battery pack gives a highly efficient use of available space.

[0085] For comparison, if 125Ah cells were used having a width of 200mm, a height of 172mm and a depth of 33mm, it might be attempted to arrange these on a shelf "end on", e.g. upright with their depth dimensions extending across the width of the pack, like books on a bookshelf. In this scenario (leaving aside for the present the issue of how the cells are to be mounted to the shelves), the depth D would be 200 mm, which via Figure 15, gives a maximum possible width W of 1920mm, which equates to 58 cells. This would give a value of A that was only 86% of the maximum achievable. Furthermore, as discussed above, it would be inconvenient to have the battery cells extend this far laterally across the TRU due to the sides of the battery pack being a convenient point for mounting fans and mounting the pack to the TRU / trailer. For instance, using 50 cells side by side to achieve a more practical overall width W would give a capacity of 20kWh (6.25kAh) per shelf, which is 15% below the arrangement of Figures 12 to 14.

[0086] The present arrangement is also convenient electrically. Each stack of cells, i.e. module, can provide 12 V. The 8 modules in each shelf can be arranged as 2 x 4 stack of cells, with each subgroup of 4 stacks of cells being connected to give 16 cells in series and overall 48V, which may be a convenient voltage for powering the refrigeration system, i.e. typical for a relatively low voltage pack. Each subgroup on each shelf may be connected in parallel to increase the battery capacity, i.e. different numbers of shelves can be provided to give different battery capacities for different applications. In other examples, a high voltage pack may be provided wherein all 96 cells are connected in series giving a voltage of 288V. It will be appreciated that other arrangements are possible, e.g. 32 or 64 cells in series. Thus, the layout of battery cells lends itself to different electrical configurations without any redesign of the packing of the cells being required.

[0087] In the present example, 3 shelves are provided. Each cell has a height of 204mm. Allowing 30mm per shelf for the thickness of the shelf and space for interconnects at the top of the cell, and a further approx. 20 mm for structural members above the battery pack and approx. 200mm for chargers mounted below the battery pack, the overall height may be between 900 mm and 950 mm. Where 736Wh (230Ah) cells are used according to the arrangement above, the battery pack may have an overall capacity of 71 kWh (22.08kAh).

[0088] Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present claims.

Claims

CLAIMS1 . A rechargeable battery pack for a transport refrigeration unit (TRU) , the pack comprising: a framework by which the pack is mounted to the TRU in use; a battery compartment for plural rechargeable battery cells, the framework including at least one shelf for supporting the plural battery cells in the compartment; wherein the cells have a width, depth and height and the width is at least twice the depth, wherein the cells are arranged on each shelf in plural groups of upright cells, each group arranged side by side on the shelf, and in each group the cells are arranged in a lateral orientation plural cells deep such that the overall number of cells form a cuboid volume on the shelf.

2. The pack of claim 1 , wherein the cells are 4 deep in a group and there are up to 8 groups per shelf.

3. The pack of claim 1 or claim 2, wherein the cells within a group are arranged in a housing, having flanges extending at the front and rear faces of the housing by which the group of cells is mounted to the shelf.

4. The pack of any preceding claim, wherein the cells have dimensions of approx, (within 2%) 174mm width, 204mm height and 54mm depth.

5. The pack of any preceding claim, the at least one shelf comprises plural, vertically spaced shelves on each of which the battery cells are so arranged.

6. The pack of any preceding claim, wherein the battery pack has vertical structural side members between the shelf or shelves extend.

7. The pack of any preceding claim, wherein the pack has a front and rear cover to seal the battery compartment.

8. The pack of any preceding claim, wherein the shelves have a fluid flow channel running through them by which the battery cells are cooled in use.

9. The pack of any preceding claim, comprising fluid movement devices mounted tothe side of the battery pack to provide fluid flow for cooling the battery cells.

10. The pack of any preceding claim, comprising mounting points at both sides of the structural framework for mounting the battery pack to a TRU or trailer, wherein the mounting points are between 1 ,7m and 1 .85m apart and the battery cells do not extend laterally as far as the mounting points.11 . The pack of any preceding claim, wherein each shelf has a capacity of at least approx. 23.5kWh.

12. The pack of any preceding claim, wherein the overall battery pack has a capacity of at least approx. 71 kWh.

13. The pack of any preceding claim when dependent on claim 2, wherein the 8 groups of cells on each shelf are arranged as 2 subgroups of 4 groups of cells, wherein the groups of cells in each subgroup are electrically connected in series.

14. A transport refrigeration unit in combination with a battery pack of any preceding claim.

Images